1. Field of the Invention
The present invention relates to a drive device and a drive method, which switches two phases according to a pulse induced voltage induced in a non-energized phase, the two phases being selected from three phases of a brushless motor and to be applied with a pulse voltage according to a pulse width modulation signal.
2. Description of Related Art
Japanese Laid-open (Kokai) Patent Application Publication No. 2009-189176 discloses a drive device for a three-phase brushless motor that measures a pulse induced voltage induced in a non-energized phase by a pulse voltage, and compares this pulse induced voltage with a threshold, to successively switch energization patterns.
However, in a sensor-less control which compares a pulse induced voltage of a non-energized phase with a threshold and thereby successively switches two phases to be applied with the pulse induced voltage, when the pulse induced voltage is decreased and does not reach the threshold due to a demagnetization failure, energization patterns cannot be switched, so that the brushless motor cannot be started up.
Although it becomes possible to start up the brushless motor by changing the threshold according to the decrease in the pulse induced voltage, the start-up failure of the brushless motor also occurs when the brushless motor is locked.
However, it has been difficult to discriminate between the demagnetization failure allowing the motor startup and the lock not allowing such startup, and therefore there has been a possibility that the control of the brushless motor might be continued in the locked state, in which the startup is not allowed.